Home > Articles > Cisco Network Technology > IP Communications/VoIP > Mastering IPv6 SLAAC Concepts and Configuration

Mastering IPv6 SLAAC Concepts and Configuration

  • Article is provided courtesy of Cisco Press.
  • Date: Dec 19, 2013.


  1. SLAAC Defined
  2. SLAAC Configuration
  3. Summary

Article Description

Some differences between IPv4 and IPv6 are more obvious than others. Sean Wilkins explains the new available methods for performing address configuration, how to implement DHCPv6 in IPv6, and the best options for stateless configuration. He also walks you through a detailed sample SLAAC configuration on a Cisco device to be sure you can apply what you’ve learned to your situation.

With a wider scale implementation of IPv6 in most companies either in progress or soon to be in progress, it’s becoming even more important for engineers to have IPv6 skills. Unfortunately, the slow roll out of IPv6 over the last decade has made a number of engineers avoid learning the topic in any great detail as the majority of companies didn’t require the skills. With the progress in IPv6 implementation, this is no longer true, and many engineers need to become up to date with these skills in short order. Continuing the series covering the most essential IPv6 skills, how they operate, and how they can be used in a working environment, this article in particular covers IPv6 Stateless Address Autoconfiguration, or SLAAC, as it is commonly referenced.

SLAAC Defined

Like IPv4, there are a number of different ways that a host can be addressed in IPv6; the two most common in IPv4 are static addressing and dynamic address configuration via the Dynamic Host Configuration Protocol (DHCP). Often the reason that engineers use DHCP is that it not only provides a method of dynamically assigning addresses, it also provides a way to assign the host devices other service information like DNS servers, domain names, and a number of different custom information.

To perform address configuration on IPv6 there are a couple of familiar methods and a few additional methods, including: static addressing, static addressing with DHCPv6 (stateless), dynamic addressing via DHCPv6 (Stateful), SLAAC alone, or SLAAC with DHCPv6 (Stateless). IPv6 static addressing works exactly the same as IPv4 static addressing so there is no mystery there. IPv6 does, however, provide two different ways of implementing DHCP, either stateful (e.g., when an IPv4 DHCP server tracks the addresses that are given out) and stateless. Stateless DHCP does not track what information is given out to clients and does not give out IPv6 addresses; instead, it provides the extra information that most people relate with typical DHCP assignment, e.g., DNS server information. Stateless DHCP is then matched up with another mechanism (such as Static addressing or SLAAC) for IPv6 address assignment.

SLAAC provides the ability to address a host based on a network prefix that is advertised from a local network router via Router Advertisements (RA). RA messages are sent by default by most IPV6 routers; these messages are sent out periodically by the router and include information including:

  • One or more IPv6 prefixes (Link-local scope)
  • Prefix lifetime information
  • Flag information
  • Default device information (Default router to use and its lifetime)

SLAAC is implemented on the IPv6 client by listening for these local RA’s and then taking the prefix that is advertised to form a unique address that can be used on the network. For this to work, the prefix that is advertised must advertise a prefix length of 64 bits (i.e., /64); SLAAC will then dynamically form a host identifier that is 64 bits long and will be suffixed to the end of the advertised prefix to form an IPv6 address. Originally, the host identifier was formed using the EUI-64 rules (the same that are used to form link local addresses) and many devices still use this method. However, some Microsoft operating systems by default do not use this original method. Instead, they take advantage of some additional privacy extensions that were defined in RFC4941.

To give an idea as to how this works, the example topology shown in Figure 1 is used.

Figure 1: SLAAC Example

If the hosts (H1-H4) shown in Figure 1 were using the EUI-64 method of host identification, the IPv6 addresses created using SLAAC would be:

  • H1 – 2000:1234:5678::12FF:FE34:5678
  • H2 – 2000:1234:5678::EBFF:FEA4:C1AE
  • H3 – 2000:1234:5678::BAFF:FE24:C4AE
  • H4 – 2000:1234:5678::84FF:FE67:AEFC

To be thorough, the EUI-64 process will be outlined for H1 as follows:

The prefix 2000:1234:5678::/64 will be learned from R1’s RA messages and will be the initial prefix.

The client identifier would then be created from the MAC address that is assigned to H1, in this case 0200:1234:5678. The first step of EUI-64 conversion is to split the MAC address in half and place FF:FE in the middle, which results in 0200:12FF:FE34:5678. Then the seventh bit will be flipped, in this case the first 8 bits is 00000010 (0x02). Next, the seventh bit is flipped and the bit becomes 0, resulting in 00000000 (0x00); this gives a final host identifier result of 0000:12FF:FE34:5678. When the prefix and the host identifier are brought together, it results in an IPv6 address that is used for H1 of 2000:1234:5678:0000:0000:12FF:FE34:5678, which can be shortened to 2000:1234:5678::12FF:FE34:5678.

2. SLAAC Configuration | Next Section

Cisco Press Promotional Mailings & Special Offers

I would like to receive exclusive offers and hear about products from Cisco Press and its family of brands. I can unsubscribe at any time.


Pearson Education, Inc., 221 River Street, Hoboken, New Jersey 07030, (Pearson) presents this site to provide information about Cisco Press products and services that can be purchased through this site.

This privacy notice provides an overview of our commitment to privacy and describes how we collect, protect, use and share personal information collected through this site. Please note that other Pearson websites and online products and services have their own separate privacy policies.

Collection and Use of Information

To conduct business and deliver products and services, Pearson collects and uses personal information in several ways in connection with this site, including:

Questions and Inquiries

For inquiries and questions, we collect the inquiry or question, together with name, contact details (email address, phone number and mailing address) and any other additional information voluntarily submitted to us through a Contact Us form or an email. We use this information to address the inquiry and respond to the question.

Online Store

For orders and purchases placed through our online store on this site, we collect order details, name, institution name and address (if applicable), email address, phone number, shipping and billing addresses, credit/debit card information, shipping options and any instructions. We use this information to complete transactions, fulfill orders, communicate with individuals placing orders or visiting the online store, and for related purposes.


Pearson may offer opportunities to provide feedback or participate in surveys, including surveys evaluating Pearson products, services or sites. Participation is voluntary. Pearson collects information requested in the survey questions and uses the information to evaluate, support, maintain and improve products, services or sites; develop new products and services; conduct educational research; and for other purposes specified in the survey.

Contests and Drawings

Occasionally, we may sponsor a contest or drawing. Participation is optional. Pearson collects name, contact information and other information specified on the entry form for the contest or drawing to conduct the contest or drawing. Pearson may collect additional personal information from the winners of a contest or drawing in order to award the prize and for tax reporting purposes, as required by law.


If you have elected to receive email newsletters or promotional mailings and special offers but want to unsubscribe, simply email information@ciscopress.com.

Service Announcements

On rare occasions it is necessary to send out a strictly service related announcement. For instance, if our service is temporarily suspended for maintenance we might send users an email. Generally, users may not opt-out of these communications, though they can deactivate their account information. However, these communications are not promotional in nature.

Customer Service

We communicate with users on a regular basis to provide requested services and in regard to issues relating to their account we reply via email or phone in accordance with the users' wishes when a user submits their information through our Contact Us form.

Other Collection and Use of Information

Application and System Logs

Pearson automatically collects log data to help ensure the delivery, availability and security of this site. Log data may include technical information about how a user or visitor connected to this site, such as browser type, type of computer/device, operating system, internet service provider and IP address. We use this information for support purposes and to monitor the health of the site, identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents and appropriately scale computing resources.

Web Analytics

Pearson may use third party web trend analytical services, including Google Analytics, to collect visitor information, such as IP addresses, browser types, referring pages, pages visited and time spent on a particular site. While these analytical services collect and report information on an anonymous basis, they may use cookies to gather web trend information. The information gathered may enable Pearson (but not the third party web trend services) to link information with application and system log data. Pearson uses this information for system administration and to identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents, appropriately scale computing resources and otherwise support and deliver this site and its services.

Cookies and Related Technologies

This site uses cookies and similar technologies to personalize content, measure traffic patterns, control security, track use and access of information on this site, and provide interest-based messages and advertising. Users can manage and block the use of cookies through their browser. Disabling or blocking certain cookies may limit the functionality of this site.

Do Not Track

This site currently does not respond to Do Not Track signals.


Pearson uses appropriate physical, administrative and technical security measures to protect personal information from unauthorized access, use and disclosure.


This site is not directed to children under the age of 13.


Pearson may send or direct marketing communications to users, provided that

  • Pearson will not use personal information collected or processed as a K-12 school service provider for the purpose of directed or targeted advertising.
  • Such marketing is consistent with applicable law and Pearson's legal obligations.
  • Pearson will not knowingly direct or send marketing communications to an individual who has expressed a preference not to receive marketing.
  • Where required by applicable law, express or implied consent to marketing exists and has not been withdrawn.

Pearson may provide personal information to a third party service provider on a restricted basis to provide marketing solely on behalf of Pearson or an affiliate or customer for whom Pearson is a service provider. Marketing preferences may be changed at any time.

Correcting/Updating Personal Information

If a user's personally identifiable information changes (such as your postal address or email address), we provide a way to correct or update that user's personal data provided to us. This can be done on the Account page. If a user no longer desires our service and desires to delete his or her account, please contact us at customer-service@informit.com and we will process the deletion of a user's account.


Users can always make an informed choice as to whether they should proceed with certain services offered by Cisco Press. If you choose to remove yourself from our mailing list(s) simply visit the following page and uncheck any communication you no longer want to receive: www.ciscopress.com/u.aspx.

Sale of Personal Information

Pearson does not rent or sell personal information in exchange for any payment of money.

While Pearson does not sell personal information, as defined in Nevada law, Nevada residents may email a request for no sale of their personal information to NevadaDesignatedRequest@pearson.com.

Supplemental Privacy Statement for California Residents

California residents should read our Supplemental privacy statement for California residents in conjunction with this Privacy Notice. The Supplemental privacy statement for California residents explains Pearson's commitment to comply with California law and applies to personal information of California residents collected in connection with this site and the Services.

Sharing and Disclosure

Pearson may disclose personal information, as follows:

  • As required by law.
  • With the consent of the individual (or their parent, if the individual is a minor)
  • In response to a subpoena, court order or legal process, to the extent permitted or required by law
  • To protect the security and safety of individuals, data, assets and systems, consistent with applicable law
  • In connection the sale, joint venture or other transfer of some or all of its company or assets, subject to the provisions of this Privacy Notice
  • To investigate or address actual or suspected fraud or other illegal activities
  • To exercise its legal rights, including enforcement of the Terms of Use for this site or another contract
  • To affiliated Pearson companies and other companies and organizations who perform work for Pearson and are obligated to protect the privacy of personal information consistent with this Privacy Notice
  • To a school, organization, company or government agency, where Pearson collects or processes the personal information in a school setting or on behalf of such organization, company or government agency.


This web site contains links to other sites. Please be aware that we are not responsible for the privacy practices of such other sites. We encourage our users to be aware when they leave our site and to read the privacy statements of each and every web site that collects Personal Information. This privacy statement applies solely to information collected by this web site.

Requests and Contact

Please contact us about this Privacy Notice or if you have any requests or questions relating to the privacy of your personal information.

Changes to this Privacy Notice

We may revise this Privacy Notice through an updated posting. We will identify the effective date of the revision in the posting. Often, updates are made to provide greater clarity or to comply with changes in regulatory requirements. If the updates involve material changes to the collection, protection, use or disclosure of Personal Information, Pearson will provide notice of the change through a conspicuous notice on this site or other appropriate way. Continued use of the site after the effective date of a posted revision evidences acceptance. Please contact us if you have questions or concerns about the Privacy Notice or any objection to any revisions.

Last Update: November 17, 2020